Inversion at Selenium in the Bis(β-diketonato)[2-(methylseleno)-ethylamine]cobalt(III) Ion
作者:Kiyohiko Nakajima、Masaaki Kojima、Junnosuke Fujita
DOI:10.1246/bcsj.59.3505
日期:1986.11
The selenide (selenoether) complexes, [Co(β-dik)2(CH3SeCH2CH2NH2)]+ (β-dik: acac=2,4-pentanedionate, Clacac=3-chloro-2,4-pentanedionate, Meacac=3-methyl-2,4-pentanedionate, and dbme=1,3-diphenyl-1,3-propanedionate) were prepared and separated into two racemic pairs of the diastereomers (Δ(R)Λ(S) and Δ(S)Λ(R) isomers). The complexes in solution epimerize by inversion at the selenium atom, and the rates were followed by high-performance liquid chromatography in the temperature range of 30.3–55.0 °C in 0.05 mol dm−3 Na2SO4 (acac, Clacac, and Meacac complexes) or in methanol (dbme complex). The ΔG25°C\eweq values for inversion of [Co(β-dik)2(CH3SeCH2CH2NH2)]+ decrease in the order β-dik=Clacac(108)>acac(106)>dbme(104)>Meacac(100 kJ mol−1), and the decrease in ΔG25°C\eweq comes mainly from a decrease in ΔH\eweq. The effect of substituents is electronic and the Hammett relationship was found to hold for the inversion rates of the acac, Clacac, and Meacac complexes.
硒化物(硒醚)[Co(β-dik)2(CH3SeCH2CH2NH2)]+(β-dik:acac=2,4-戊二酸酯,Clacac=3-氯-2,4-戊二酸酯,Meacac=3-甲基-2,4-戊二酸酯,dbme=1,3-二苯基-1,3-丙二酸酯),并将其分离为两对非对映异构体(Δ(R)Λ(S)和Δ(S)Λ(R)异构体)。在 0.05 mol dm-3 Na2SO4(acac、Clacac 和 Meacac 复合物)或甲醇(dbme 复合物)中,在 30.3-55.0 °C 温度范围内,溶液中的复合物通过硒原子上的反转发生二聚反应,并通过高效液相色谱法跟踪反应速率。[Co(β-dik)2(CH3SeCH2CH2NH2)]+的反转ΔG25℃eweq值按照β-dik=Clacac(108)>acac(106)>dbme(104)>Meacac(100 kJ mol-1)的顺序降低,ΔG25℃\eweq的降低主要来自ΔH\eweq的降低。取代基的影响是电子性的,而且发现 Hammett 关系在 acac、Clacac 和 Meacac 复合物的反转速率上是成立的。